1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to elevator systems in which the speed of an elevator car is controlled by a speed pattern generator.
2. Description of the Prior Art
U.S. Pat. No. 3,774,729, which is assigned to the same assignee as the present application, discloses an elevator system in which a speed pattern generator controls the speed of an elevator car by providing a time based speed pattern TRAN which accelerates the elevator car to, and then maintains, a predetermined running speed. When the elevator reaches a predetermined position relative to a target floor, the speed pattern generator substitutes a distance based speed pattern DSAN for the time based pattern, to control the speed of the elevator car during the slowdown phase of the run.
In order to provide a high quality ride, without noticeable "bumps" in the elevator car during a run, the transfer from the time based or running speed pattern to the distance based slowdown speed pattern must be stepless, i.e., the patterns should match at transfer time.
In the hereinbefore mentioned U.S. Patent, pattern transfer from the running speed pattern TRAN to the slowdown speed pattern DSAN is initiated after the running speed pattern has entered a slowdown phase, with transfer occurring when the running speed pattern reaches a preset maximum deceleration rate. Excellent performance is achieved when the pattern magnitudes match at the time of transfer, and the deceleration rate of the slowdown speed pattern is the same as the predetermined maximum deceleration value which was used to initiate pattern transfer. This ideal condition is rarely achieved because car response is not perfect and the time based speed pattern generator has some error which may cause the initiation of "turn-around" at the incorrect time. The term "term-around" refers to the transition interval from constant acceleration to constant deceleration, if the car has not yet reached constant velocity, or the transition interval from constant velocity to constant deceleration when it has. Thus, the running and slowdown patterns do not exactly match at transfer time, causing a "bump" to be felt by passengers in the elevator car. "Blending" the two speed patterns at pattern transfer time, as taught in U.S. Pat. No. 3,651,892, which is assigned to the same assignee as the present application, provides some improvement, but if turn-around is started as much as 0.2 second early, a bump is still felt in the car at pattern transfer, even when the signals or patterns are blended.
Copending application Ser. No. 073,822 filed Sept. 10, 1979, entitled "Elevator System", now U.S. Pat. No. 4,261,439, which is assigned to the same assignee as the present application, discloses an improvement for the elevator system of U.S. Pat. No. 3,774,729 in which the slowdown speed pattern DSAN is forced to match the running speed pattern TRAN prior to transfer between the speed patterns. Prior to pattern transfer, the invention of the copending application also automatically and continuously determines the deceleration rate to be used by the slowdown speed pattern after transfer. The value of this deceleration rate at the precise time of transfer is used to decelerate the elevator car at a constant rate. This deceleration rate cuases the slowdown speed pattern to have a predetermined value when the elevator car is at a predetermined location relative to the target floor, enabling stepless transfer at this predetermined location from the slowdown speed pattern DSAN to a landing speed pattern HTAN, which is initialized to the predetermined value. While this arrangement provides a very smooth transfer from the running speed pattern to the slowdown speed pattern, it does introduce another variable into the system, i.e. the variable slope of the slowdown pattern curve, which can be different on each run. While the control system is constructed to operate correctly with an adaptable deceleration rate, this additional variable is another error source which may lead to errors in pattern transfer from the slowdown pattern to the landing pattern. Thus, it would be desirable to improve the pattern transfer arrangement of U.S. Pat. No. 3,774,729, without changing the slope of the slowdown speed pattern curve.
The present invention improves upon the pattern transfer arrangement of U.S. Pat. No. 3,774,729, while maintaining the constant slope aspect of the slowdown speed pattern, by making the turn-around of the time-based running speed pattern adaptive, and thus non-critical. The turn-around will always be smooth and the approaches of the car to the target floor consistent.